Why are there extra deform bones in rigify armature?
As said, this is to improve your weight painting in case of mesh flipping issues during twist movments.
You can modify the number of limb segments produced by the metarig in Bone Properties &gt; Rigify Type.
For example, if I set the left arm Limb Segments to 1:

The metarig will produce a rig with 2 segments per metarig bone for the right arm and only one for the left: